AD 79-02-06    Exhaust System

January 25, 1979

This AD affects a group of ’78 and ‘’79 152s, and A152s..

Another cracking muffler …. maybe. For this one, look up the tailpipe. If you see nothing, that’s good no further action required. If you see a perforated baffle, that could be bad depending on the model. If it’s an Elano muffler, it’s ok. If it’s a KMR muffler, it needs to be repaired or replaced.

79-02-06 CESSNA: Amendment 39-3395. Applies to Cessna Model 152 (Serial Numbers 15279406 through 15282919) and Model A152 (Serial Numbers A1520735 through A1520845) airplanes having Cessna original equipment type exhaust systems installed.

COMPLIANCE: Required as indicated unless already accomplished.
To preclude contamination of cabin heater air with carbon monoxide, accomplish the following:

A) Before next flight, except that the airplane may be flown with the cabin heat in the “OFF” position to a location where this inspection may be accomplished:

1. Unless previously accomplished per AD 78-21-01, visually inspect the clearance between the exhaust pipe and cowl opening. Minimum clearance must be .375 inch in the fore and aft direction and .625 inch in the lateral direction with a smooth transition between. Enlarge cowl opening as required to obtain this clearance.

2. Visually inspect the interior of the heater muffler, through the tailpipe, for the presence of a perforated baffle system using a flashlight or other aid to illuminate the interior of the heater muffler. If no baffle system is present, the heater muffler is acceptable and the further inspections and actions required by paragraph A)3 of this AD are not required. If an internal baffle system is present, remove the cowling to gain access to the exhaust system. Determine whether the exhaust system is a KMR Industries Part Number 1-1000, or an Alternate Elano Part Number EL099001-060 by examination of the nameplate which is located between the hose connections on the aft side of the heater shroud on the KMR system or comparison of the exhaust system configuration with those depicted in Figures 64 and 65 of the Model 152 and A152 Illustrated Parts Catalog. If the system is the Alternate Elano system, the present heater muffler is acceptable and the further inspections and actions specified in paragraph A)3 of this AD are not required.

3. If the exhaust system is a KMR Industries assembly:

a) Prior to further flight, safety wire the cabin heat valve control arm in the closed position by securing it to the engine mount using .032 diameter safety wire.

b) Within the next 10 hours time-in-service and within each 50 hours time-in-service thereafter:

1. Remove the engine cowling and the KMR Industries heat exchanger shroud.

2. Using a 5-power, or greater, magnifying glass, visually inspect the heater muffler can for any cracks around the tailpipe and along the three lines of spot welds on the surface of the heat exchanger can itself.

3. If the heater muffler can is found cracked, prior to next flight:

(i) Replace it with a heater muffler having a serial number 4000 or above; or

(ii) Repair and reinstall heater mufflers having cracked or completely pulled-through spot welds and/or closed cracks that do not extend under the end plates and do not exceed 3 inches continuous length, by heli-arc welding in accordance with the following:

1. Use rod material compatible with titanium stabilized 321 stainless steel.

2. It is not necessary to reattach the can to the baffle at pulled-through spot welds if the can and baffle are separated. In this case, it is only necessary to close the hole or crack in the can at the spot weld location.

3. Disconnect the hose between the heat exchanger shroud and the firewall cabin heat valve at the cabin heat valve and safety wire it to the engine mount tube so that 1.5 inches of the hose extends below the fuselage through the cowl air exit hole and to the right of the nose gear. Install the hose clamp on the valve end of the hose so that it grips the wire supported section of the hose. Route the safety wire between the clamp and the hose to secure the clamp and hose to the engine mount.

4. After installation of a new KMR Industries heater muffler having a serial number 4000 or above, obliterate the existing exhaust system serial number located on the nameplate attached to the shroud.

B) Upon installation of a KMR Industries heater muffler can having a serial number 4000 or above and incorporation of a dam in the heat exchanger shroud in accordance with Cessna Service Kit 152-3, the cabin heat system may be reactivated and the inspection required by Paragraph A)3.b) discontinued.

NOTE: (The serial number will be stamped on a flange of the replacement heat exchanger can.)

C) Any equivalent method of compliance with this AD must be approved by the Chief, Engineering and Manufacturing Branch, FAA, Central Region.

Cessna Service Letter SE78-71 dated December 1, 1978, or later revisions, pertains to this subject.

This AD supersedes AD 78-21-01 which became effective October 6, 1978 (43 FR 49298, 49299) to all persons except those to whom it had already been made effective by airmail letter from the FAA dated September 18, 1978.

This amendment becomes effective on January 25, 1979 to all persons except those to whom it has already been made effective by airmail letter from the FAA dated December 1, 1978